Driving force control system for four-wheel drive vehicles

Abstract

There is disclosed a driving force control system for a four-wheel drive vehicle, which is capable of properly controlling the execution and cancellation of a lock mode in which the engagement forces of clutches for distributing a driving force to auxiliary drive wheels are made maximum, thereby reducing frequency and duration of the lock mode. Further, there is disclosed a driving force control system for a four-wheel drive vehicle, which is capable of properly controlling the engagement forces of clutches for distributing a driving force of the main drive wheels to auxiliary drive wheels, thereby causing the clutches to efficiently operate without waste of power. When the vehicle is determined to be in a predetermined low vehicle speed condition, and at the same time, the shift lever of the transmission is detected to be in any of predetermined low-speed shift positions, execution of a lock mode is permitted in which the clutch engagement forces are controlled to lockable ones which can lock the main and auxiliary drive wheels to each other. When the driving force of the main drive wheels is lower than a predetermined value, the clutch engagement forces for the lock mode are limited to smaller ones than the lockable ones.

Description

[0001] 1. Field of the Invention[0002] This invention relates to a driving force control system for a four-wheel drive vehicle, which controls the engagement forces of clutches to thereby control the drive forces distributed to auxiliary drive wheels.[0003] 2. Description of the Prior Art[0004] A driving force control system of this kind has been proposed by the present assignee in Japanese Laid-Open Patent Publication (Kokai) No. 10-194005, for a four-wheel drive vehicle including left and right front wheels as main drive wheels, and left and right rear wheels as auxiliary drive wheels. The engine of the vehicle is connected to the left and right front wheels via an automatic transmission, a front differential, and left and right front drive shafts. Further, the front differential is connected to the left and right rear wheels via a transfer, a propeller shaft, a rear differential, and left and right drive shafts.[0005] The driving force control system includes left and right elect...

AI Technical Summary

Benefits of technology

This solution reduces the frequency and duration of lock mode execution, conserves electric power, and enhances clutch durability by limiting engagement forces according to actual driving conditions, thereby improving fuel economy and drivability.

Problems solved by technology

However, the conventional driving force control system is configured such that the lock mode is unconditionally executed when the lock switch is operated.

Therefore, if the driver operates the lock switch without the knowledge of the function of the lock switch or by mistake, the lock mode is unnecessarily executed.

As a result, during this lock mode, the maximum amount of current continues to be supplied to the electromagnetic clutches to waste the electric power, and further fuel economy is degraded due to traveling of the vehicle in the four-wheel drive mode, which is fuel-consuming and, in this case, unnecessary.

This can adversely affect the drivability as well, depending on the conditions of the vehicle.

Further, the clutches are operated at their maximum engagement forces frequently and over extended time periods, so that the durability of the clutches is also degraded, which will offer an obstacle to the reduced size of electromagnetic clutches.

Despite the fact, the vehicle continues to be in the lock mode in which the maximum clutch engagement forces are generated, and hence a large amount of electric power is wastefully consumed due to supply of the maximum amounts of current to the electromagnetic clutches.

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